CLAY SOILS

CLAY SOILS derive their character from the aluminic silicate which they contain in a state of mixture, as well as in chemical combination with other substances. Some soils contain so large a proportion of alumina as 35 per cent., but generally the proportion is much smaller. The feldspars which chiefly yield the alumina of clay soils contain also soda, potash, and lime, substances which tend to render clays fertile when under cultivation. The physical characters, however, of the different varieties of clay soils arising from the varying proportions of silica, and other substances mixed with the alumina, are chiefly concerned in their relative fertility. Calcareous matter exercises a considerable influence on their powers of producing crops. For an account of the distribution of soils in this country, see Johnston's and Cameron's Elements of Agricultural Chemistry and Geology.